High-frequency resonators with excellent temperature characteristics using edge reflection

Michio Kadota, Tetsuya Kimura

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Currently, some surface acoustic wave (SAW) devices, especially duplexers, are required to have a good temperature coefficient of frequency (TCF), because the bands between a transmission band (Tx) and a receiving band (Rx) of the duplexer such as Personal Communication Services (PCS) mobile phone in US is very narrow (about 1%). However, a 36-48°YX-LiTaO 3 substrate, which is used for most SAW radio frequency (RF) filters and most SAW duplexers in mobile phone systems, has an optimum electromechanical coupling factor for their applications but does not have a good TCF. It was reported that the TCF of a transversal SAW filter using thin Al electrodes on LiTaO 3 and LiNbO 3 substrates with negative TCF was improved by depositing thick SiO 2 film with positive TCF on them. However, most RF SAW filters and most duplexers are composed of resonator type SAW devices such as laddertype or multi-mode resonator type filters using thick Alelectrodes on the substrate to obtain a large reflection coefficient. When the thick SiO 2 films were deposited on the SAW resonator and the multi-mode SAW resonator filter consisting of thick Al-electrodes/36°YX-LiTaO 3 to improve their TCF, their frequency characteristics were markedly deteriorated. Because their coupling factor becomes smaller and their propagation loss larger due to large periodic convex portions as thick as the Alelectrodes produced on the SiO 2 surface. To avoid influence due to these large periodic convex portions, a SiO 2 with thin convex/thin Al-electrodes/LiTaO 3 and a flattened SiO 2 without convex/thick Al-electrodes/LiTaO 3 structures were examined, but they didn't show good characteristics because of the small reflection at the grating reflectors. On the other hand, it is considered that the reflection of a shear horizontal (SH) wave at a substrate edge of the SiO 2 /Al-electrodes/LiTaO 3 structure is large regardless of Al or SiO 2 thickness, because the SH wave completely reflects at the free substrate edge. But, it has been considered that it is difficult to form a fine substrate edge for a high-frequency resonator using the edge reflections. This time, by developing of forming method for a fine substrate edge, high-frequency edge reflection type resonators with a good TCF and an excellent frequency characteristic, which were composed of a thick SiO 2 with thin convex/thin Al-electrodes/ 36°YX- LiTaCO 3 and a flattened thick SiO 3 without convex/thick Al-electrodes/36°YX-LiTaO 3 , have been realized for the first time.

Original languageEnglish
Title of host publication2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum, FCS
Pages154-159
Number of pages6
DOIs
Publication statusPublished - 2007 Dec 1
Event2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum, FCS - Geneva, Switzerland
Duration: 2007 May 292007 Jun 1

Publication series

NameProceedings of the IEEE International Frequency Control Symposium and Exposition

Other

Other2007 IEEE International Frequency Control Symposium Joint with the 21st European Frequency and Time Forum, FCS
CountrySwitzerland
CityGeneva
Period07/5/2907/6/1

ASJC Scopus subject areas

  • Engineering(all)

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